Giant buttercup is estimated to cost farmers on average about $1000 a hectare each year in lost production and sprays, which Rose equates to $85,000 for his farm. He says that’s “pretty signifi cant” for a small family farm.
Cows avoid the toxic leaves leaving the plants well alone to dominate the surrounding grass struggling beneath it. Herbicides knock it back but Rose says they also hammer the pasture by as much as 30% for a couple of months that would usually be the peak growth period on a dairy farm.
This means he doesn’t have the surplus growth for supplements and there’s the problem of resistance. The emerging resistance to herbicides in giant buttercup prompted the three year project that includes AgResearch field trials in Golden Bay. Though there’s a range of different herbicide products on the market to fight giant buttercup they span only four modes of action (MOA) which means farmers need to know the MOA in each herbicide and rotate the MOA each year to avoid resistance.
“Giant buttercup has a very waxy coat which is genetically different to the buttercup it used to be,” Rose says.
“It has evolved to become more resistant and if we can kill half the buttercup in the paddock after a spray I’m happy now.”
The farm carries the 230-cow herd through winter and while grasses are destroyed in the mud the giant buttercup rhizome stays intact to dominate regrowth in the paddock.
In the past Rose says droughts knocked the buttercup back each year and kept some control over it but irrigation installed to boost production also boosts buttercup growth year-round.
“These days you really have to spray every year and that’s really not sustainable so we’re keen on alternatives being developed.”
Once a giant buttercup has evolved resistance to a particular mode of action (MOA) none of the herbicides with that MOA – such as MCPA and MCPB – will have an effect on the weed, AgResearch scientist Graeme Bourdot says. His research shows buttercup populations that have become resistant to MCPA and MCPB will take about 28 years to become susceptible again. And the regression back to susceptibility would happen only if the farmer stopped using those herbicides.
If farmers are rotating sprays annually through the four available MOAs they will use the same MOA only every fi fth year. If they sprayed buttercup every second year MOA rotation could allow them to use the same MOA once every nine years and Bourdot says resistance would be very unlikely.
Information on the MOAs and giant buttercup control is available at the new AgPest site (formerly PestWeb) at www.agpest.co.nz and results from the Golden Bay trials will be updated on to this website as the three-year trial progresses.
The project is cash-funded by the Sustainable Farming Fund, DairyNZ and Ravensdown with in-kind funding from Dow AgroSciences, the Taranaki and Southland regional councils plus Tasman District Council.
